1. Field of the Invention
The present invention relates in general to a brake pedal apparatus, and more particularly to an improvement of a lever-ratio switching type brake pedal apparatus in which a characteristic of a lever ratio is changed depending upon a depressing force.
2. Discussion of Prior Art
There is known a brake pedal apparatus having: (a) an operating pedal which is disposed on a support member pivotably about a first axis, and which is to be operatively depressed by an operator; (b) a pivot member which is disposed on the support member pivotably about a second axis parallel to the first axis, and which is mechanically connected to the operating pedal so as to be pivoted about the second axis in response to a depressing operation effected on the operating pedal; and (c) an output member which is to be mechanically pressed or pulled as a result of pivot motion of the pivot member. As an example of such a brake pedal apparatus, Patent Document 1 discloses an apparatus in which the operating pedal and the pivot member are connected to each other through a cam, which provides a high degree of freedom in setting a lever-ratio characteristic. The lever-ratio characteristic is a characteristic of change in a moment-length ratio (lever ratio) in relation with a pedal stroke (depressing amount) of the operating pedal, namely, is a characteristic of change in a lever ratio (corresponding to a ratio of output amplification to a depressing force applied to the operating pedal) in relation with the pedal stroke.
Further, there is proposed a brake pedal apparatus having: (a) an operating pedal which is to be operatively depressed by an operator; (b) a switching lever which is disposed on a support member pivotably about a first axis, and which supports the operating pedal such that the operating pedal is pivotable relative to the switching lever about a second axis parallel to the first axis; (c) a positioning device which mechanically positions the switching lever in a predetermined reference position about the first axis, and which allows the switching lever to be pivoted away from the reference position about the first axis when a reaction force acting on the second axis during the depressing operation effected on the operating pedal exceeds a predetermined switching load; and (d) an engaging member which causes the operating pedal (pivoted about the second axis) to be brought into engagement with the switching lever in a predetermined relative position when the switching lever is pivoted, and which causes the operating pedal to be pivoted integrally with the switching lever about the first axis. As an example of such a brake pedal apparatus, Patent Document 2 discloses an apparatus in which, when the operating pedal is strongly depressed, for example, in the event of failure of a boosting device such as a brake booster, a center of pivot motion of the operating pedal is shifted from the second axis to the first axis, whereby the lever-ratio characteristic is switched to another lever-ratio characteristic. It is therefore possible to increase the ratio of the output to the depressing force and accordingly to generate a further increased braking force, as a result of the shift of the center of the pivot motion from the second axis to the first axis, where a relationship such as a positional relationship between the first and second axes is established such that the lever ratio is increased by the shift of the pivot motion center from the second axis to the first axis. In this arrangement in which the lever-ratio characteristic per se is switched to another lever-ratio characteristic, the lever ratio can be changed more largely than in the arrangement disclosed in the above-described Patent Document 1.
Patent Document 1: JP-H5-185912A
Patent Document 2: JP-2002-347590A
However, in such a conventional lever-ratio switching type brake pedal apparatus having a construction arranged to change the center of pivot motion of the operating pedal that is operatively depressed by an operator, possible errors in dimensions and position of each component of the apparatus are likely to cause variation of a home position of the operating pedal (i.e., an initial position of the operating pedal when it is not operated) and/or provide the operating pedal with play. Thus, for avoiding such a problem, a high degree of dimensional accuracy of the components and a high degree of assembling accuracy of the components are required. Further, in the conventional lever-ratio switching type brake pedal apparatus, the degree of freedom in setting the lever-ratio characteristic is low since the lever ratio is changed by merely changing the center of the pivot motion of the operating pedal.
The present invention was made in the light of the background art discussed above. It is therefore an object of the invention to make it possible, in a brake pedal apparatus in which a lever-ratio characteristic is switched to another depending on a depressing force applied to the operating pedal, to restrain variation of a home position of the operating pedal and play of the operating pedal even in presence of errors in dimensions and position of each component of the apparatus, and to increase the degree of freedom in setting each of the lever-ratio characteristics that are selectively available, for providing a lever ratio that is further suitably variable according to the depressing force.